In either DC power feeding or AC power feeding, an arc discharge occurs at power off. In the case of AC, since there is an instant at which the voltage becomes zero at every predetermined time (for example, every 10 milliseconds), the arc discharge stops spontaneously at least within the above-described predetermined time (for example, within 10 milliseconds). In DC power feeding, however, the arc discharge does not stop spontaneously since there is no instant at which the voltage becomes zero.
Therefore, technologies for the purpose of suppressing occurrence of an arc discharge at power off in the case of DC power feeding have been disclosed (see Patent Literature 1, Patent Literature 2 and the like).